The present disclosure relates to the subject matter disclosed in the German patent applications Nos. 100 00 954.9 and 100 01 337.6, both of Jan. 17, 2000, and No. 100 24 976.0 of May 19, 2000, the entire specifications of which are incorporated herein by reference and from which priority is claimed.
The invention relates to a monitoring device for checking for a predefined position of a body or for checking for the presence of a body, comprising a pivotal checking element, a motor for driving the checking element and a control device for controlling the pivotal movement of the checking element.
Monitoring devices of this type are known, for example, from DE 30 03 431 C2, DE 43 10 872 A1 or DE 196 08 628 A1.
They are employed in machine tools for example in order to check whether a tool, such as a drill for example, is still in a predefined position or, for example, has broken off, or for checking as to whether a xe2x80x9cforeign bodyxe2x80x9d has entered a region in which such a body would constitute a disturbance.
In DE 30 03 431 C2, it is proposed, for the purposes of setting the sensitivity or impact weight on the tool or workpiece of a sensing needle which is seated in the checking element, that the rotational speed of a dc motor and hence the pivotal speed of the sensing needle be altered. Herein, a microcomputer controls the rotational speed and this would be reduced at a predefined number of angular steps prior to a stored reference angular position.
The object of the invention is to improve a monitoring device of the generic kind in such a manner that, commencing from the state of the art, the pivotal movement of the checking element will be effected in a controlled manner in order to be able to set the monitoring device in a universally simple manner.
In accordance with the invention, this object is achieved in a monitoring device of the type described hereinabove in that the control device specifies or indicates the pivotal position of the checking element in dependence on the time.
Firstly, it is thereby known where the checking element is located at any time within the control precision range, and secondly, for every pivotal position, it is known how much time was needed for the checking element to arrive at this position. Hereby, in particular, those times are fixed (within the control precision range) which the checking element needs in order to reach a monitoring region and for passing through the monitoring region. The time, which is needed for detecting a body or for detecting the absence of a body, is thereby fixed and hence not subject to variations. Likewise, the time, which a checking element needs for returning to its starting position, is fixed and varies, at most, within the control precision range. The latter, however, can be determined during the manufacture of the monitoring device in accordance with the invention and, in particular, can be set so small that in practice it is not discernible.
In accordance with the invention, a monitoring device is provided which has constant sampling times, for example, when monitoring tools. Consequently, the monitoring process is not subject to any form of disturbance caused, for example, by the sampling times becoming shorter or longer. In particular, the pivotal movement of the checking element is independent of the xe2x80x9cpre-historyxe2x80x9d of the checking element; larger or smaller frictional moments, which can always occur during the operation of the monitoring device, are compensated by the control of the pivotal movement provided in accordance with the invention by adjusting to a predefined pivotal position-time course in such a manner that the pivotal position of the checking element at a certain time point will lie at a predefined set location.
It is advantageous that the pivotal movement of the checking element be controlled in accordance with a predefined position-time course. Such a course can be produced by the manufacturer and, in particular, programmed into the control device. It is thereby ensured that the checking element will be in defined pivotal positions at defined times.
It is expedient for the controlled value for controlling the pivotal movement of the checking element to be the pivotal position of the checking element at a predefined time, i.e. the controlled value is the predefined course of position against time. In this manner, the time, which is needed for detecting a body or for monitoring a monitoring region, can be set so as to be substantially free of variations.
It is especially advantageous if the pivotal position of the checking element relative to a starting position is known at every time in the pivotal movement of said checking element. A control loop can thereby be formed for effecting a comparison between a reference pivotal position and the actual detected pivotal position so as to move the checking element on the basis of the result of the comparison in such a manner that the pivotal movement will follow a predefined pivotal position-time course as closely as possible.
It is expedient if the time needed by the checking element for its pivotal movement from a first pivotal position into a second pivotal position is fixed. The times, which a monitoring device needs for carrying out a monitoring process, are thereby defined substantially free of variations. It is especially advantageous if the time, which the checking element needs for its pivotal movement commencing from a starting position until arriving at a checking position, is fixed. Furthermore it is advantageous if the time, which the checking element needs for its pivotal movement commencing from a starting position until arriving at a reversal position, is fixed. It is thereby ensured that a monitoring process in accordance with the invention will be effected within a defined time interval.
Furthermore, it is expedient if the time, which the checking element needs for its pivotal movement from a reversal position until arriving at the starting position, is fixed. The time, after which the monitoring device in accordance with the invention will again be ready for use, is thereby defined precisely, i.e. when it is once more in its starting position from which a monitoring process can take place.
The monitoring device in accordance with the invention can be utilised in an extremely simple manner if the predefined position-time course is stored in the control device. The user does not then have to be concerned about appropriate settings, and the monitoring device has fixed times for carrying out the monitoring processes.
In one advantageous variant of an embodiment, a control value (setting value) is a time increment. It is also advantageous if a control value is a pivotal position increment or a pivotal position decrement. The pivotal path of the checking element can be varied in this manner, as can the speed of the checking element by forming a differential quotient and likewise, in a corresponding manner from the formation of a further differential quotient, its acceleration.
Advantageously, the control value is formed, in dependence on a predefined maximum torque. As will be referred to again hereinbelow, it is advantageous if the torque of the checking element is limited so as to prevent it impinging heavily on a body, thereby possibly causing damage thereto or even the destruction thereof. The torque of an electric motor is proportional, in particular, to the control current for the electric motor. Due to the fact that the maximum permissible torque is used for generating the control value, such a torque limiting process can be achieved in a simple manner.
It is especially advantageous if the magnitude of path intervals and/or time increments for the control of the pivotal position of the checking element are matched to the predefined position-time course. It can be advantageous, especially when arriving in a monitoring region, if the control and regulating process is carried out with increased accuracy. This can be achieved, inter alia, by reducing the size of the corresponding path increments and time increments. In certain circumstances, larger path intervals or time increments can be defined outside the monitoring region where large variations in regard to the position-time course are not expected.
In order to define the pivotal position of the checking element in dependence on the time, the control device expediently comprises a position control device which compares the actual pivotal position at a certain time with a reference pivotal position and produces a control value signal in dependence on the result of the comparison. The difference between the reference pivotal position, especially in accordance with a predefined position-time course, can thereby be compared with the actual real position at any time and a correction can be carried out within the framework of a regulating loop in correspondence with the difference between these two positions.
It is expedient if the position control device comprises a PD controller. The path can thereby be corrected simultaneously with respect to a path difference and with respect to a speed difference.
In order to prevent a hard impact between the checking element and a body, it is especially advantageous if the control device comprises a torque control device which compares the actual motor current with a reference motor current and produces a control value signal in dependence on the result of the comparison. In essence, the motor current indicates the torque of the motor. In accordance with the invention, it is then ensured that, due to the comparison with a reference motor current, and especially with a maximum permissible motor current (corresponding to the maximum permissible torque), the motor current will lie below a maximum permissible value thereby preventing heavy impact between a checking element and a body being monitored.
From a constructional point of view, it is expedient if the torque control device comprises a P controller. A control value signal, which is proportional to the difference between the reference motor current and the actual motor current, is provided by means of this P controller.
Expediently, there is provided a motor driver which controls the motor in dependence on one or more control values. The checking element can thereby be moved into a specific pivotal position at a specific time point, whilst simultaneously keeping the torque below a predefined maximum value. It is advantageous if the motor driver produces a pulse width modulated signal for controlling the motor. The pulse width modulated signal contains information regarding the control current for the motor, by means of which the torque of the motor is decided, and also regarding a control voltage, by means of which a motor position and hence a pivotal position of the checking element is defined.
It is especially very advantageous, if there is provided a control value limiter to which control value signals delivered by the position control device and the torque control device are supplied for producing a single torque-limiting control value signal. The control value limiter then ensures that the motor driver makes available such a signal, particularly a pulse width modulated signal, to the motor, as will thereby ensure that the torque of the motor and hence that of the checking element will lie below a predefined maximum torque.
It is particularly advantageous if the checking element is pivotal commencing from a starting position through a transition region into a monitoring region in which the predefined position of the body lies or in which the presence of a body should be monitored, and in that the control device limits the torque of the checking element in such a manner that the maximum possible torque in the monitoring region is reduced relative to that in the transition region. By virtue of this inventive concept, it is firstly ensured that the checking element will reach the monitoring region quickly, i.e. that it can pass through the transition region with a high torque value. Secondly, in the monitoring region, the checking element will strike a body that is possibly located therein with a small amount of torque since the maximum possible torque has been reduced. The checking element will exert a force on the body even when its speed is zero i.e. it is resting on the body. By reducing the torque limit, it is ensured, in accordance with the invention, that this force will not be too large and, in particular, will not exceed a force which could destroy the body, such as a tool for example.
Account should be taken of the fact that, if the pivotal movement of the checking element is stopped by a body in the monitoring region, the control device will attempt to counteract this, i.e. the torque will be increased for a short period despite the reduction in speed. The body, on which the checking element then rests, may thereby be subjected to an increased load. Since the control process for the pivotal movement of the checking element has a certain time constant, such a short term rise in torque cannot generally be prevented. However, by virtue of the solution in accordance with the invention, whereby there is a predefined upper limit for the torque in the monitoring region, this being reduced relative to the upper limit in the transition region, the torque will be prevented from exceeding a certain value and hence the force on the body will also be prevented from exceeding a certain value.
A sensing needle is preferably arranged on the checking element. The torque will alter in correspondence with the differing lengths of the sensing needle. However, by virtue of the solution in accordance with the invention, it is always ensured that the torque will not exceed an upper limiting value independently of its actual value.
Furthermore, in accordance with the invention, provision may be made for a seal to be arranged between the checking element and the housing. A frictional moment is exerted by this seal which counteracts the torque of a shaft which is driven by the motor. The absolute value of the torque may thereby alter in this case too. However, in accordance with the invention, it is always ensured that an upper limit for the torque will not be exceeded.
It is especially very advantageous if the motor is a dc motor and if the control device limits the supply of current to the motor. The torque, which the motor can exert, is set by the current through the motor. If the supply of current is limited, then the maximal permissible amount of torque can be set in a simple manner, and, in particular, the maximum permissible torque can be correspondingly reduced by reducing the supply of current in the monitoring region.
It is especially very expedient if the pivotal movement of the checking element is controlled by means of a combined position, speed and torque control and regulating arrangement. The pivotal movement can then be matched to the demands, and in particular, the transition region can be passed through quickly and the predefined position of a body in the monitoring region can be monitored without fear of damaging or even destroying the body.
It is expedient for the speed of the checking element to be reducible during its passage from the transition region into the monitoring region so as to produce the requisite control of the monitoring process in the monitoring region.
It is especially very expedient if the reduction of the torque limit is effected after the reduction in the speed of the checking element. On the one hand, it is thereby ensured that the speed of the checking element will be reduced in the monitoring region and, in particular, that the reduction of the torque limit will not prevent the speed sinking to a predefined value, but, on the other hand, it is nevertheless ensured that the checking element will not strike against a body in the monitoring region with too great a torque.
It is especially very advantageous if an angle transmitter is provided for detecting the position of the checking element. This may, in particular, be a digital angle transmitter and incremental transmitter. The pivotal movement of the checking element can then be controlled in a simple manner and, in particular, a control loop can be formed in which the pivotal position of the checking element is regulated along a predefined position-time course in time-dependent manner.
It is expedient if the transition region comprises an acceleration region in which the speed of the checking element is increased commencing from the starting position. Commencing, in particular, from the rest position of the checking element, this thereby permits its speed to increase rapidly so that it can pass through the transition region in a rapid manner.
Moreover, it is advantageous if the transition region comprises a braking region in which the speed of the checking element is reduced. In a simple manner, this arrangement permits the checking element to be pivoted in the monitoring region at a lower speed than in the transition region so as to prevent a hard impact between the checking element and the body that is to be monitored.
It is expedient for the speed of the checking element to be maintained substantially constant between an acceleration region and a braking region of the transition region. This thereby results in improved control and regulating possibilities since the pivotal angle is proportional to time in this region, and improved control and regulating possibilities are also created since non-linear calculations do not need to be carried out in this region whereby the setting behaviour for the controlled value when such regulation is required will then be improved because of the linear relationship between the pivotal angle and the time.
It is also particularly advantageous if the speed of the checking element is maintained substantially constant in the monitoring region. In essence, the reasons for this are the same as were indicated immediately above.
It is especially expedient for the control of the pivotal movement, if the control device carries out the speed and torque control by means of time-dependent controlling of the position of the checking element. The position can be directly determined from the output of the digital angle transmitter, and since a specific pivotal angle will be turned through in specific intervals of time, the time increments can also be determined in a simple manner. By forming the corresponding quotient, the speed of the checking element can be determined at least to a first approximation. It is particularly advantageous here, if the control device indicates the pivotal position of the checking element. Furthermore, it is advantageous if the control device indicates the pivotal speed of the checking element.
It is especially very advantageous if via the control device a learning (teach in) cycle for detecting the monitoring region is performable. By virtue of such a learning cycle, it can be determined where the transition region, through which the checking element should pivot quickly, ends, and where the monitoring region, in which the torque limit is reduced, should begin. In particular, the corresponding angular values, which separate the two regions from each other, do not have to be entered directly, but the monitoring device in accordance with the invention will itself determine where the boundaries lie. It is expedient, if a plurality of predefined position-time courses is stored in the control device and if a specific position-time course is selected in dependence on a monitoring region that has been detected in a learning cycle. The curves may be stored directly or be obtained by means of a calculating rule which will allow an associated curve to be calculated from the learned positions.
It is expedient if the monitoring region is set by the control device such that it begins at a certain angular amount prior to a body detected in the learning cycle. This angular amount may be 5xc2x0 or 10xc2x0 for example. Optimal subdivision of the whole pivotal region of the checking element can thereby be obtained, in that, it is ensured on the one hand, that the checking element will pass quickly through the transition region, and on the other hand, that accurate monitoring will be ensured in the monitoring region in which the predetermined position of the body lies or in which it should be monitored as to whether a xe2x80x9cforeign bodyxe2x80x9d is located therein.
It is expedient for stop means to be provided for limiting the pivotal movement of the checking element. An internal reference position for the monitoring device in accordance with the invention can thereby be made available and it cannot be displaced.
Expediently, for the purposes of setting a reference position of the checking element, this is moved at a predefined speed into a stop position in which the corresponding stop means touch. An unaltered reference position is thereby made available.
Expediently, for the purposes of defining the reference position of the checking element in the stop position, the corresponding stop means are rotated against one another at low torque. It is thereby possible, for this touching of the stops, which is necessary for defining the reference position, to be effected in a defined manner and thus allow the reference position to be precisely determined.
The monitoring device in accordance with the invention, can be employed in xe2x80x9cdifficultxe2x80x9d working conditions if a seal is arranged between the checking element and a shaft by means of which the checking element is driven.
Such an inventive seal prevents working fluids or swarf or other impurities from penetrating into the region between the shaft and the checking element and/or between the shaft and the housing. Metal swarf may, for example, become trapped between the housing and the checking element in such a manner as to hinder the rotation of the shaft. Such processes will interfere with the operation of the monitoring device i.e. it will not be able to perform its real task, checking for a predefined position of a body or checking for the presence of a body. The seal arranged in accordance with the invention will prevent metal swarf, in particular, from reaching the shaft. In addition, since an additional seal is provided, the sealing of the housing relative to the exterior space will be improved. The monitoring device in accordance with the invention will thereby be less susceptible to disturbances and the downtime, in which the operation of the monitoring device is interrupted and hence it can no longer perform its real task, will be much reduced. Moreover, metal swarf can perforate the shaft seal in the housing so that fluid may enter into the interior of the housing. The additional seal provided in accordance with the invention completely prevents metal swarf from reaching the shaft seal.
It is particularly very advantageous if the seal abuts the checking element and abuts the housing. The intrusion of swarf and/or fluids into the region between the checking element and the shaft and/or between the housing and the shaft is thereby prevented.
It is advantageous for the seal to be formed symmetrically about an axis and especially about a rotational axis of the shaft. A substantially angle-independent frictional moment can thereby be obtained, especially during the rotational movement of the checking element, thereby achieving simpler control of the pivotal movement of the checking element.
It is particularly very expedient if the seal is seated between the checking element and the housing co-axially relative to the shaft.
It is expedient for an intermediate space to be formed between the shaft and the seal. Consequently, the seal itself does not abut on the shaft and will not hinder its rotational movement.
In an advantageous variant of an embodiment, provision is made for the seal to be rotationally fixed relative to the checking element. The seal is thus carried along by the checking element during the pivotal movement of the checking element whilst it will rotate relative to the housing.
Basically, it is also conceivable for the seal to be rotationally fixed relative to the housing and then to rotate the checking element relative to the seal. However, the proposed variant is more expedient from a constructional point of view since a seal must be provided around the shaft in the housing in order to seal the entrance for the shaft through the housing. The corresponding annular space is not available for the arrangement of a mounting element for the seal between the checking element and the housing. By contrast, a further seal for the checking element itself does not need to be provided apart from the seal between the checking element and the housing.
Expediently, the checking element comprises a mounting element for the seal onto which the latter can be put in order to fix it non-rotationally relative to the checking element. An easily manufacturable, easily releasable but nevertheless sealed connection between the seal and the checking element in accordance with the invention can thereby be achieved in a simple manner.
From a manufacturing point of view it is particularly expedient if the mounting element is formed by a mounting ring through which the shaft is guided and onto which the seal is adapted to be put. The seal can thereby be arranged completely around the shaft in a simple manner.
Furthermore, it is expedient to provide an annular recess for accommodating the seal between the mounting element and the checking element. An abutment face for an end-face of the seal is made available by such an annular recess, and in addition, the seal can rest in full area contact on an outer surface of the mounting ring. The seal is thus connected to a large surface area of the checking element so that a good sealing effect is thereby achieved.
Expediently, the outer diameter of the seal substantially corresponds to the diameter of the checking element so that, firstly, a large abutment face for the seal is available on the checking element and secondly, material will not be wasted unnecessarily.
It is particularly very expedient if the seal comprises a packing ring for the purposes of putting it onto the checking element. Good sealing properties between the seal and the checking element are achieved by virtue of such a packing ring.
Furthermore, it is particularly very advantageous if the seal comprises a collar having a V-shaped sealing lip which abuts on the housing. Good sealing properties are achieved between the seal and the housing by virtue of such a sealing lip, and the spacing between the checking element and the housing can be varied by means of the sealing lip without the need to provide a plurality of seals for this purpose, since, to a certain extent, the V-shaped sealing lip allows the axial extent with reference to the direction of the rotational axis to be set.
It is expedient if the collar is rotatable with the checking element relative to the housing.
In order to obtain good sealing properties between the seal and the housing on the one hand, and in order to be able to vary the spacing between the checking element and the housing on the other, it is advantageous if the outer surface of the collar is substantially in the form of a truncated cone at least when force is not being applied thereto in the axial direction. An imaginary cone peak of the V-shaped collar points towards the checking element. Thus, when the axial spacing between the checking element and the housing becomes smaller, the collar can spread in a radial direction so that the effectiveness of the seal will not worsen despite the change in this spacing.
It is expedient if the inner surface of the collar is in the form of a truncated cone at least when force is not being applied thereto in the axial direction. This ensures that the sealing lip will be in full area contact with the housing even when the spacing between the checking element and the housing becomes smaller thereby achieving good sealing properties.
It is expedient if an axial extent of the seal can be varied by the collar so that the monitoring device in accordance with the invention can be employed in variable manners and is particularly economical.
Further features and advantages of the invention form the subject matter of the following description taken in conjunction with the sketched illustration of the embodiment.